This invention relates to air conditioning system evaporators in general, and specifically to a novel air fin arrangement therefor.
Vehicle air conditioning evaporators, because of their placement near the interior of the vehicle, are subject to having the film of water that naturally condenses thereon blown out and into the vehicle interior by the forced air stream that is blown through the evaporator, a phenomenon generally referred to as spitting. Typical evaporator cores consist of a vertically oriented plurality of tubes or plates, through which cold refrigerant is pumped, and between which corrugated air fins or xe2x80x9cair centersxe2x80x9d are brazed, in close thermal contact. The air centers are cooled by contact with the cold tubes or plates, and warm, humid air is cooled as it is blown over the corrugated fins. Water naturally condenses on both the outside of the tubes/plates and the fins. It is relatively easy to promote drainage of condensed water off of the tube surfaces, since they are vertically oriented, and drainage channels can be stamped or formed into the surface thereof if desired.
Promoting drainage from the corrugated fins is more difficult. Since the corrugations are oriented substantially horizontally, so as not to block the horizontal air flow thereover, the fin walls inevitably block vertical downward flow of condensed water. The corrugated fin walls typically have louver patterns cut through them, to break up the otherwise laminar airflow, and these provide some drainage vertically through the fin walls, but louver cuts are quite thin, and the surface tension of the water film resists rapid drainage through such thin openings. Louvers also are typically not cut all the way to the fold or crest of the fin walls, so condensate will naturally pond in the horizontal troughs created by the horizontal fins brazed to the vertical tube surfaces. It has been proposed to drain these troughs by cutting special drainage holes through the fin wall folds, near the areas of contact with the tube surfaces. This inevitably reduces fin cooling efficiency, by reducing the conductive contact between tube and fin, and makes the fin more difficult to produce. Other proposed schemes include stacking two layers of corrugated fins between the tubes, each layer separated from the other by either a porous sheet, or by a thin corrugated sheet in which the corrugations are arranged 90 degrees to the fin walls, creating a less impeded vertical drainage path. This requires an additional part, and creates a core that is more difficult to stack and braze, because of the double layer of air fins. Either shorter air fins have to be used, or the refrigerant tubes have to be spaced twice as far apart, which would seriously reduce efficiency. Such a design would also do nothing, in and of itself, to drain the horizontal troughs at the tube outer surfaces.
When standard air centers are used, with no special drainage enhancing features beyond the existing louvers, the standard means to reduce so called xe2x80x9cspittingxe2x80x9d of undrained condensed water out of the evaporator core is the provision of a screen over the downstream face of the core. This adds expense and increases air pressure drop, but is commonly used.
The subject invention promotes drainage from the air centers or fins not by altering the design of the fin per se, but by a unique combination of orientations of the fins between the plates. Nothing is changed in the fin""s basic design, or in the basic manufacture and assembly of the core itself.
In the preferred embodiment disclosed, pairs of vertically oriented evaporator plates are spaced apart a standard distance. Rather than a single, continuous corrugated fin between each adjacent pair of plates, a compound arrangement of a leading fin and trailing fin is used, of equal, standard height and conventional configuration, but with 90 degree opposed orientations. Specifically, the fin walls of the leading fin are oriented horizontally, as is conventional, but the leading fin covers less than half of the depth of the core, about one third as disclosed. The remainder of the core comprises a similarly shaped fin oriented 90 degrees opposite.
Air entering the leading face of the core travels between the fin corrugations conventionally, parallel to the fin walls. While there is no direct vertical drainage path out of the leading fin, condensation is not heavy in that area, since the air has not yet cooled enough, for the most part, to reach the dew (condensation) point. Once through the leading fin, the air encounters the vertically oriented trailing fin and the vertically oriented fin walls thereof. Resistance to air flow is higher now, but not completely blocked, since air can still flow through the louver patterns of the successively encountered vertical fin walls. The air is sufficiently cooled by the time it passes through the trailing fins to condense the entrained water, which can now flow easily downwardly under the force of gravity, out of the core. The folds of the trailing fin, being vertically oriented, now create vertical drainage channels, rather than non draining horizontal troughs. Since the fins are standard design and standard height, differing only in their compound orientation between the tubes, very little change to the standard core assembly and construction is needed.